Alloys, consisting of a base metal and one or more other metals or non-metals, are prepared in order to alter the mechanical or chemical properties of the base metal. For example, alloying may be performed to induce hardness, toughness, ductility, corrosion resistance, or other desired properties into the base metal. In practice, alloys are formulated and used to produce cast or wrought metal parts having certain desirable properties which correspond to their end uses. Aluminum (Al) and magnesium (Mg) alloys are commonly used to make cast or wrought automotive parts, such as sand cast engine blocks, because these nonferrous alloys are relatively light weight and corrosion resistant (compared to cast iron or steel).
The presence of impurities, however, in these alloy compositions can significantly impact the mechanical and chemical properties of the alloy parts. For example, elemental iron is considered an impurity in aluminum alloy parts used in the automotive industry because, in high concentrations, iron reduces the ductility and tensile strength of the alloy part. In magnesium alloys, iron is also considered an impurity because it renders the alloy part more susceptible to corrosion. High-purity metals, such as aluminum and magnesium, however, are not readily available. Therefore, these metals and their alloying elements may need to be refined or purified before downstream casting or forming processes.
One method of removing iron impurities from aluminum or magnesium alloys is by heating the alloys to form melts, and then precipitating iron-rich inter-metallic particles, also known as “sludge,” from the melts. In this method, iron-rich inter-metallic phases are formed within the melts by adding certain metal elements, such as manganese, chromium or zinc, to the melts. The melts are then cooled to initiate nucleation and crystallization of iron-containing inter-metallic particles from the iron-rich phases. The iron-containing particles precipitate from the melts and are then removed, for example by gravity separation or filtration.
However, the amount of manganese, chromium, or zinc added to each melt is critical to the formation of sludge, but is difficult to control. Additionally, methods of separating precipitated particles from melts of aluminum or magnesium are inefficient and any metals added during the precipitation process that remain in the melts can adversely affect the mechanical and chemical properties of the cast alloy parts. There is therefore a need for a more efficient method of effectively removing iron from aluminum or magnesium alloys.